(1) Field of the Invention
The present invention relates to a method of manufacturing a foot warming exothermic device and the foot warming exothermic device. More particularly, the invention relates to a method of manufacturing a foot warming exothermic device which can easily produce an ultrathin foot warming exothermic device at low cost by placing a fluid exothermic composition on a wrapper at high speed, can securely fix a portion or the whole of the exothermic composition in the wrapper and prevent movement thereof, and can well conform to the user's foot configuration and efficiently warm a desired site of the foot when it is applied to the site, and to the foot warming exothermic device.
(2) Description of the Related Art
In recent years, exothermic devices of the type known as disposable body warmers have been widely used such that the exothermic device includes an exothermic composition enclosed in a flat pouch comprised of a gas permeable or gas-tight thin sheet base material and a gas permeable thin sheet covering material.
It is also common to use an exothermic device having an adhesive layer attached to one side of a pouch of the above noted type such that the exothermic device can be pasted directly or through underwear to the skin of a living body. Further, it has been proposed to utilize as a hot compress an adhesive layer with a wet pack medication incorporated or carried therein, or as a medication-containing layer with a skin absorbable medication incorporated or carried therein (see Japanese Patent Application published specification No. 2-149272).
As an old saying goes, "cooled head and warmed feet", it has been believed that warming feet is a key to good health. With widespread use of such exothermic devices, therefore, foot warming exothermic devices for warming the sole of the foot have now become commercially available. Various foot warming exothermic devices of this type have been proposed including, for example, those disclosed in Japanese Patent Application published specifications Nos. 2-154762, 2-172460, 5-115310, Japanese Utility Model Applications published Nos. 6-21616 and 5-84317, and Japanese Patent Application published No. 5-176951.
In manufacturing such a foot warming endothermic device it is general practice to place an exothermic composition of powder form with some water content on a predetermined site in a base material and then cover the same with a gas permeable covering material. Thereafter, the base material and a peripheral edge portion of the covering material are sealingly bonded by heat sealing or with a hot melt adhesive over and along the entire peripheral edge portion.
Such a foot warming exothermic device of the prior art includes an exothermic composition containing, in traditionally appropriate proportions, a metal powder, such as iron powder, and water, and in addition an activated carbon for accelerating heat generation, a metal chloride for fracturing an oxide film on the surface of the metal powder and continuously generating an exothermic reaction,and a water retainer for preventing a sticky effect of the composition. The exothermic composition is in the form of a water-containing powder and is placed on a base material.
In the case where the exothermic composition, with all its ingredients mixed together in an appropriate blend ratio as above noted, is placed on the base material, the trouble is that after the blending of the ingredients into the exothermic composition and before the foot warming exothermic device is enclosed in an outer pouch, an exothermic reaction occurs which results in a loss of exothermic energy and a quality degradation of the exothermic composition. Furthermore, a reaction product resulting from the exothermic reaction involves various harmful effects, such as decreased yield, handling inconvenience, complicated maintenance-related problems, limitations affecting machine operation time as well as operator working hours, and difficulties involved in dealing with coagulated matter.
While the exothermic composition is provided through its water content with a wetting characteristic, the proportion of the water content is so low as to be suitable for an exothermic reaction, so that the exothermic composition assumes a powder form and has only poor fluidity. This poses a problem that it is extremely difficult to allow the composition to be uniformly distributed within a predetermined area on the base material through mere placement of the same in position. In view of this fact, it is common practice to equalize the distribution of the exothermic composition to some extent by means of a roller or the like during the process of covering the composition with a covering material and sealing the same. With such a method, however, the distribution of the exothermic composition tends to become inclined toward the source of pouch material. In order to increase the proportion of the exothermic composition distributed in the direction of pouch material feed, it is necessary to increase the height of a chamber defined within the pouch, thereby making it possible to eliminate any offset in the distribution of the exothermic composition as by manual shaking at the time of use.
Where the foot warming exothermic device becomes thicker in its entirety, the device feels rough and has poor hand. Moreover, the device has inferior flexibility so that it is unable to well conform to any complex surface irregularity at an application site and/or any curved surface of a small curvature. The thickness increase also results in a degradation in the extensibility or stretchability characteristic of the device, which in turn may result in a deformation due to the wearer's movement and a lower capability of conformance to such movement.
Furthermore, as already mentioned, foot warming exothermic devices of the prior art are such that although the exothermic composition is provided through its water content with wetting characteristics, the proportion of the water content is so low as to be suitable for an exothermic reaction, so that the exothermic composition assumes a powder form and has only poor fluidity. Therefore, it is extremely difficult to cause the exothermic composition to be uniformly distributed within a predetermined area on the base material, so that the thickness of the foot warming exothermic device is irregular. As such, when the device is used in such a condition that it is affixed to an application site, continued use of the device as affixed to the same application site may be a cause of a low temperature burn.
With foot warming exothermic devices of the prior art, it is impossible to completely prevent any possible displacement during the process of manufacture or in the course of transportation in the current status of the art.
Such foot warming exothermic device, prior to use, is transported for delivery in a condition such that it is packaged within an outer pouch (preservation pouch). In this stage of transport, the exothermic composition is movable within the exothermic device and, from the standpoint of safety maintenance, it has been taken as an important requirement that the device be kept uniform in thickness so as to enable the device to exhibit a constant temperature profile throughout its entirety. In the current practice, therefore, any such device in which the exothermic composition is non-uniformly distributed is returned as an off-standard product in the stage of distribution, or is replaced upon request from the user. Hence, it is very important to secure thickness uniformity with respect to the exothermic composition in the stage of transportation.
In Japanese Patent Application Laid-Open No. 62-347, a method for adhesively fixing an exothermic composition in position is proposed. In actual manufacturing operation, however, it is almost impossible to adhesively fix an exothermic composition in powder form within a pouch. Even if such adhesion could be done, the adhesion would be too weak to enable the composition to be well fixed in position, and therefore the composition, while in use, may become peeled off or may become a plate-like mass having little flexibility, thus causing an uncomfortable feeling to the user. Furthermore, the presence of the adhesive hinders contact of the composition with air, resulting in an uneven temperature distribution and/or temperature variations. As such, this method is unsatisfactory for practical use.
Therefore, the inventor has made intensive research in order to solve the above-mentioned technical problems thereby to develop a method of manufacturing a foot warming exothermic device which can inhibit any exothermic reaction of an exothermic composition and prevent any possible heat loss due to heat generation during a manufacturing operation and various harmful effects of quality degradation and solidification of the exothermic composition, and can manufacture ultra-thin exothermic devices at a high rate, and which permits the exothermic composition to be uniformly distributed and fixed within a pouch thereby to prevent any movement and/or displacement of the exothermic composition and suppress an excessive exothermic reaction of the composition.
It has been found as a result that the heating principle of an exothermic device of this type is based on a heat generation occurring with the oxidation of a metal powder, and the rate of this oxidation, or exothermic reaction, is greatly influenced by the quantity of water in particular.
That is, to promote this oxidation, an appropriate 10 degree of moisture is the key, the reaction is markedly retarded if moisture is too much or too little. A good balance between necessary moisture and air (oxygen) supply is said to maximize the rate of oxidation or exothermic reaction.
Too little moisture results in a shortage of moisture necessary for the reaction though air is sufficient. Too much moisture results in barrier layers of moisture to diminish air supply, thereby retarding the reaction.
The inventor has found that use of a fluid exothermic composition, that is, an exothermic composition made viscous, makes it possible to manufacture an ultra-thin exothermic device at a high rate of production because the composition can be easily transferred by printing, e.g., screen printing, or coating, and that since any excess moisture forms barrier layers of moisture to diminish air supply thereby to substantially stop any exothermic reaction in progress, any quality degradation of the exothermic composition in process and various harmful effects of the solidification of the composition can be prevented.
The inventor has also found that by causing an exothermic composition to be formed into a viscous fluid configuration, the exothermic composition can be uniformly distributed within a pouch by printing, e.g., screen printing, or coating, and that when the fluid exothermic composition is transferred or laminated on a water-absorbable foamed film sheet, paper, corrugated board, cardboard core paper, nonwoven cloth, woven cloth, or porous thin sheet, or on a water absorptive layer formed on such material, the fluid exothermic composition can be fixed in position on such foamed thin sheet, nonwoven cloth, woven cloth, or porous thin sheet, or on the water absorptive layer formed thereon, being thereby prevented from movement.
Further, the inventor has found that use of a printing technique, such as screen printing, or a lamination technique, such as coating, enables the formation of the exothermic device to a very thin configuration, which results in a decrease in the rate of exothermic reaction per unit time, whereby an excessive exothermic reaction of the exothermic composition can be suppressed. Additionally, the inventor has found that where a fluid exothermic composition is laminated on a Wrapper material, e.g., paper, card board, card board core, or nonwoven cloth, such as of rayon, by using a printing technique, such as screen printing, or a coating technique, the stage of powder inputting can be eliminated in the process for manufacturing an exothermic device, which simplifies the process of factory management which must be carried out to the satisfaction of the GMP standards in the manufacture of medical tools and devices and medicament supplies in the future.
Further, the inventor has found that when part of the moisture content of a fluid exothermic composition in which the proportion of water is relatively high is absorbed into a wrapper material, such a base material and/or covering material, barrier layers go out of existence, whereby any possible harmful effect of excessive moisture can be eliminated.
Further, the inventor has found that a fluid exothermic composition acts to adhesively join the base material and the covering material together and bites into rough surfaces of the base material and the covering material and, therefore, that through such anchoring effect of the exothermic composition, any possible displacement of the composition within the exothermic device can be prevented not only in the manufacturing process, but also in the stage of distribution and during use by the consumer.
Conventional foot warming exothermic devices have a drawback that heat generation cannot completely be controlled. In some cases, an abrupt temperature rise (to about 90.degree. C.) may occur when the user puts off his shoes, with the result that the duration of heating becomes extremely short. Depending upon the type of shoes and/or individual physical constitution, such devices often involve problems of insufficient heat generation and burn due to excessive heating. There are many who suffer from foot cold and a great need exists for a safe foot warming exothermic device.
The temperature of the foot sole is associated with blood stream and is influenced by changes in ambient temperature, such as atmospheric temperature, in delicately varied degrees, depending upon sole temperature changes during morning, day time, and night time, changes in physical condition, meals, and the quantity of exercise. Of course, this is not the same with all people, there being considerable difference among individuals.
Further, there are many factors affecting heat generation, including type of shoes, type of socks, whether the shoe is tight or loose, and in condition of heat insulation. Even if the conditions for heat generation are kept constant, where the conditions are favorable for heat generation, there may be a danger of excessive heating, which means a danger of burn. Whilst, where the conditions are unfavorable for heat generation, there may be unsatisfactory heat generation, thus the device is rendered useless.
In contrast to conventional foot warming exothermic devices, with respect to a foot warming exothermic device having an exothermic composition incorporated therein by transfer, it has been found that even if the proportion of iron powder, a heat generating material, is increased to 60% in weight ratio to the total of all ingredients, air barrier layers (moisture-containing layers) in a fluid which cover the iron powder or heat generating material can become air permeable as moisture is deprived of them as a result of an exothermic reaction of the iron powder since the transfer of the exothermic composition is effected by using a thickener. Furthermore, air supply can be gradually obtained through the surface of the device. Thus, a stable heat generation can be obtained, and if conditions for heat generation are changed, still a favorable heat generation can be obtained.